1. Field of the Invention
The present invention relates to a sheet processing device, and an image forming apparatus.
2. Description of the Related Art
For sheet processing, such as aligning, sorting, stacking, stapling, folding, and punching sheet-type recording media including recording sheets, transfer sheets, overhead projector (OHP) sheets, sheets need to be aligned in a sheet-conveyance direction and in a direction perpendicular to the sheet-conveyance direction. To aid alignment of sheets in the sheet-conveyance direction, a rear-end fence is provided upstream in the sheet-conveyance direction for the trailing edge of the sheets to rest against, whereas a pair of aligning members (commonly known as jogger fences) are provided for aligning the sheets in the direction perpendicular to the sheet-conveyance direction by supporting the two lateral edges of the sheets.
For performing sheet processing such as stapling, it is important that the edges of sheets are aligned and pressed flat by a pressing member or the like. The use of such a pressing member would entail timing adjustment to avoid the pressing member getting in the way of a stapler. The timing adjustment ultimately affects productivity.
Several technologies are known for enhancing the level of preparedness of sheets for stapling. For example, Japanese Patent Application Laid-open No. H11-130338 discloses a conventional sheet processing device that includes a stapling tray for receiving and stacking sheets ejected from an image forming apparatus, a rear-end fence for supporting and aligning the edges of the sheets in a sheet-conveyance direction, and a stapler for stapling an edge of the sheet bundle aligned by the rear-end fence. The conventional sheet processing device further includes a regulating member that is movable in a thickness direction of the sheet bundle stacked in the stapling tray, and adjusts the distance from a sheet-loading surface of the stapling tray for guiding the sheets to the rear-end fence.
Japanese Patent Application Laid-open No. 2000-327208 discloses another conventional sheet processing device, integrally including a post-process tray, a conveyance path for guiding sheets towards the post-process tray, and a conveying member. The sheets in the post-process tray are ejected to a sheet discharge tray after stapling process, etc. The conveyance of the sheets is disallowed in the reverse direction beyond a predetermined spot in the conveyance path, and the sheet(s) that have crossed the predetermined spot is kept resting in a stand-by path provided downstream of the predetermined spot. The sheet(s) are conveyed on the stand-by path towards the post-process tray after stacking on them the next sheet that is conveyed via the conveying path. With this, productivity in image formation can be prevented from lowing without increasing the complexity and the size of the device or the cost involved.
Japanese Patent Application Laid-open No. 2004-182399 discloses a compact sheet processing device which can perform center stapling with high reliability and at low cost. The sheet processing device includes processing units for performing predetermined processes after image formation. The processing units include a stacker, aligning members, a first conveying member, a stapler, a moving member, a second conveying member, a folding member, and a retracting member. The stacker stacks thereon the sheets. The aligning members align the sheet bundle by pressing the downstream edge of the sheets flush against a first sheet-bundle regulating member in the sheet-conveyance direction as well as in a direction perpendicular to the sheet-conveyance direction. The first conveying member conveys the sheet bundle aligned by the aligning members to a second sheet-bundle regulating member. The stapler staples the sheet bundle, and the moving member moves the stapler in the direction perpendicular to the sheet-bundle conveyance direction. The second conveying member conveys the sheet bundle to a folding point after it is bound by the stapler and its downstream edges in the conveyance direction are aligned. The folding member folds the sheet bundle at the folding spot, and the retracting member retracts the first sheet-bundle regulating member from the path of the stapler.
However, in the conventional sheet processing devices described above, the stapler is kept positioned at the stapling position at all times and during aligning of sheets in an edge stapling process. Consequently, the edge of the sheets on the stapling side is unable to be pressed down by a pressing member. To enable the edges of the sheets on the stapling side to be pressed down, the stapler needs to be removed from the path of the pressing member during the alignment process, and brought back to the stapling position after the alignment process. However, this leads to a drop in productivity.